The Oswego Project is a prospective, longitudinal study designed to determine whether prenatal exposure to polychlorinated biphenyls (PCBs) compromises cognitive development. An established database of intrauterine (cord blood and placenta) polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDE), mirex, hexachlorobenzene (HCB), lead, erythrocyte protoporphyrin (EP), and hair mercury, as well as a host of behavioral measures, are on file for all 202 children in the project. Additional demographic, substance use, and labor/delivery variables containing well over 50 potentially confounding variables are interleaved with the analytic database. These data, combined with low participant attrition over the past 12 years, permit us to assess the impact of PCBs on cognitive development and scholastic achievement in the early teenage years. Specific Aims: 1) To determine if response inhibition is the behavioral mechanism underlying the sustained polychlorinated biphenyl (PCB)-related deficits on continuous performance and operant tasks seen at 4, 8, and 10 years of age. The Oswego project has strong evidence that prenatal polychlorinated biphenyl (PCB) exposure is associated with impulsive responding on operant and continuous performance tasks across development; evidence that suggests a deficit in response inhibition. The Oswego Project will continue to bolster these results by administering repeated continuous performance task measures at 13 years of age; 2) To determine if executive functions dependent on response inhibition are impaired by prenatal PCB exposure. Response inhibition is necessary for the proper execution of several "downstream" executive functions, which are dependent upon inhibition for their proper execution. Poor inhibitory control results in failure to protect cross-temporal responses from interfering responses, emotions, or events. Drawing from Barkley's model (1997, 1999), the Oswego Project will analyze several executive functions (Working Memory, Regulation of Affect, Reconstitution, and Internalization of Speech) to continue strengthening our results that suggest that prenatal PCB exposure impairs the response inhibition that is integral to proper execution of these functions; and 3) To determine if prenatal polychlorinated biphenyl (PCB) exposure impairs global cognitive functioning (IQ) and scholastic performance. Recent data from the Oswego Project indicate that prenatal PCB exposure predicts impaired global cognitive functioning (IQ) at 9 years of age. The pattern of deficits on the global cognitive functioning (IQ) subscales is identical to that observed in the Lake Michigan cohort. The Oswego Project will assess the stability of this association by re-administration of the Wechsler Intelligence Scale for Children at 15 years of age. In addition, school records for each child's New York State mandatory testing of English Language Arts and Math will be obtained for comparative analysis.